Industrial storage tanks used to contain fluids such as liquids or compressed gases are common and are vital to industry. Storage tanks may be used to temporarily or permanently store fluids at an on-site location, or may be used to transport fluids over land or sea. Numerous inventions pertaining to the structural configurations of fluid storage tanks have been made over the years. One example of a non-conventional fluid storage tank having a cube-shaped configuration is found in U.S. Pat. No. 3,944,106 to Thomas Lamb, the entire contents of which is incorporated herein by reference.
There has been a progressive demand for the efficient storage and long distance transportation of fluids such as liquid natural gas (LNG), particularly overseas by large ocean-going tankers or carriers. In an effort to transport fluid such as LNG more economically, the holding or storage capacity of such LNG carriers has increased significantly from about 26,000 cubic meters in 1965 to over 200,000 cubic meters in 2005. Naturally, the length, beam and draft of these super carriers have also increased to accommodate the larger cargo capacity. The ability to further increase the size of these super carriers, however, has practical limits.
Difficulties have been experienced in the storage and transportation of fluids, particularly in a liquid form, by ocean carriers. A trend for large LNG carriers has been to use large side-to-side membrane-type tanks and insulation box supported-type tanks. As the volume of the tank transporting the fluid increases, the hydrostatic and dynamic loads on the tank containment walls increase significantly. These membrane and insulation types of tanks suffer from the disadvantage of managing the “sloshing” movement of the liquid in the tank due to the natural movement of the carrier through the sea. As a result, the effective holding capacity of these types of tanks has been limited to either over 80% full or less than 10% full to avoid damage to the tank lining and insulation. The disadvantages and limitations of these tanks are expected to increase as the size of carriers increase.
The prior U.S. Pat. No. 3,944,106 tank was evaluated for containment of LNG in large capacities, for example, in large LNG ocean carriers against a similarly sized geometric cube tank. It was determined that the '106 tank was more rigid using one third the wall thickness of the geometric cube. The '106 tank further significantly reduced the velocity of the fluid, reduced the energy transmitted to the tank and reduced the forces transmitted by the fluid to the tank, resulting in substantially less deformation of the tank compared to the geometric cubic tank. It was further determined, however, that the '106 configured tank could be improved.
Additional cubic-shaped tank designs have been developed for LNG and compressed natural gas (CNG). Details of these tanks can be found in US Patent Application Publication Nos. 2008/0099489 and 2010/0258571 assigned to the assignee of the present invention, the entire contents of both publications are incorporated herein by reference.
Therefore, it would be advantageous to design and fabricate storage tanks for the efficient storage and transportation of large quantities of fluids such as LNG across land or sea. It is further desirable to provide a storage tank that is capable of being fabricated in ship yards for large LNG Carriers. It is further advantageous to provide a modular-type tank design which facilitates design, fabrication and use in the field.